Variable inductance device



Jan. 25, 1949. L. H. LYNN 2,460,138

VARIABLE INDUCTANCE DEVICE Filed June 27, 1945 Inventor; Lambert H. Lynn,

by 24423;. 8 M

His Attorney.

Patented Jan. 25, 1949 2,480,138 VARIABLE INDUCTANCE DEVICE Lambert H. Lynn, General Electric New York Scotia, N. Y., aulznor to Company,

a corporation of Application June 27, 1945, Serial No. 801,887

My invention relates to variable inductance devices, and more particularly to variable induct- .ance devices of the iron core type.

It is well known that resonant circuits comprising inductance and capacitance may be tuned to resonance at various desired frequencies by varying either the capacitance or the inductance in the circuit. It has also been recognized that, for certain applications, particularly at relatively high frequencies, inductance variation tuning possesses definite advantages over capacitance tuning. One known method of inductance variation is by means of a magnetizable iron core or slug mounted for relative axial movement with respect to the inductance coil. While iron core or slug tuning-of this type is desirable from many viewpoints, the range of inductance variation attainable is somewhat limited, so that iron core inductance tuning has been most useful in applications where the desired range of frequencies to be tuned is relatively small.

Accordingly, it is a general object of my invention to provide a new and improved variable inductance device of movable iron core type.

It is a more particular object of my invention to provide a movable iron core variable inductance device having a wide range of inductance variation.

It is a still further object of my invention to improve the attainable range of inductance variation without appreciably increasing the size of movable iron core variable inductance devices.

My invention will be more fully understood and its objects and advantages further appreciated by referring now to the following detailed specificati-on taken in. conjunction with the accompanying drawings, in which Figs. 1 and 2 are side elevations, partly in section, of variable inductance devices illustrating various embodiments of my invention, and Fig. 3 is a sectional view of another embodiment of my invention.

Referring now to the drawing, and particularly to Fig. 1, I have shown therein a variable inductance device comprising a coil I, helically wound upon a hollow supporting cylinder 2 of suitable insulating material and provided with a magnetizable core 3 relatively movable in an. axial direction. The core 3 may be formed of any suitable magnetizable material, but is preferably composed of a comminuted magnetic material, such as powdered iron or iron alloy. The core 3 is fixedly mounted at one end upon a suitable base or chassis 4 and extends into the movably mounted hollow coil spool 2 to an extent determined by the position of the spool.

7 Claims. (Cl. 177777) 2 The spool 2 is carried at one end of a threaded shaft 5 which is mounted in an internally threaded supporting sleeve 6 fixed to the base 4. The

threaded shaft 5 is provided at its other end with a knurled adjusting knob I by manipulation of which the coil I may be moved axially with respect to the magnetizable core 3.

Electric connection to the iron core end 01' the coil I is made through a slip ring a mounted upon the air core end of the spool 2 and attached to the opposite end of the coil. electrically connected to the base 4 through a spring contact 9 attached to the base and having an arm parallel to the rod 5 along which the ring 8 is slidable.

In order to increase the range of attainable inductance variation without increasing the size of the apparatus, I provide means for electrically disabling, such as by short-circuiting or opencircuiting that portion of the coil I which extends beyond the unsupported end of the iron core 3. For this purpose, a variable electric contact element, such as a roller I0 is fixedly mounted upon an insulating bracket II attached to the base 4 and is arranged to engage the coil I at a point immediately adjacent the unsupported end of the core. If the turns of the coil are widely spaced, as shown in. the drawing, it is desirable that the roller contact only one turn of the coil and that the pitch of the coil be substantially the same as the pitch of the thread on the shaft 5. In other instances, however, it may be of advantage to permit the roller to engage a greater number of turns, while coil pitch of the. shaft thread.

In operation, current is supplied to the coil I through lead wires i2 and I3 connected to the base 4 and roller I0, respectively. It will be evident that. as the coil spool 2 is rotated in a clockwise direction, the core 3 is withdrawn from the coil (due to the left-hand thread conventionally illustrated) while the roller Ill traverses the turns of the coil electrically to disable that portion of the coil beyond the end of the core Thus, the unused portion 01 the coil is provided with a core enmoosed largely of air, while only the operative portion of the coil is provided with a low reluctance magnetizable core. In this way, large inductance variations may be attained with coils of sm ll size and limited range of movement.

may differ from that At' F 2. I have shown another embodiment I of my invention in wh ch the limits of inductance variat on are even further increased by providing the disabled or unused portion of the coil with a core of non-magnetic electric conducting mate- The slip ring 8 is acearae rial, such as copper. aluminum, brass, or

core has a reluctance even greater than that of air, so that the inductance of the unused portion of the coil is even further decreased.

As shown at Fig. 2, the core has a total length substantially twice the length of the coil 8, and is composed of two sections of substantially equal length, 3a and 3b. The core section 3a, is magnetizable and is preierably formed of comminuted magnetic material, such as powdered iron or iron alloy, and the core section so is formed of copper or other non-magnetizable electric conducting material. The coil spool 2 is considerably longer than the coil l in order to accommodate the nonmagnetic section 32) of the core when the entire coil surrounds the magnetizable section to. The electric contact roller 8 engages the coil i at a point approximately adjacent the end of the iron core section to. Thus, the operative coil portion on one side of the roller is provided with an iron core, while the unused coil portion on the opposite side of the roller is provided with a copper core. In all other respects, the embodiment of Fig. 2 is similar to that of Fig. 1 and like parts have been assigned the same reference numerals.

At Fig. 3, I have shown another embodiment of my invention magnetically similar to that shown at Fig. 1, but in which the core, rather than the coil, is movable longitudinally and the unused portion of the coil is short-circuited rather than open-circuited. In this arrangement a base It carries a pair of spaced apart upright insulating supports l6 and I1. A hollow insulating coil spool I8 carrying a helical coil I9 is fixedly mounted at one end of an operating shaft 20 which carries at its other end an adjusting knob 2| and is rotatably mounted in a metallic sleeve 22 in the support [1. -The coil I9 is connected at one end to the operating shaft 20 by a lead. 23 and at the other end to a slip ring 24 by a lead 25. The slip ring 24 is mounted at the end of the coil spool l8 adjacent the support I! and is connected to a contact terminal 26 in the support I! by a contact spring 21 mounted upon the support and arranged slidably to engage the slip ring 28.

The support It carries a rod 28 disposed in alignment with the operating shaft 20 and extending into the hollow coil spool l8. Slidably mounted upon the rod-28 is a core 29 preferably formed of comminuted iron. The core 29 is constrained to move longitudinally of the coil l9 as the coil spool is rotated. For this purpose, I provide a pulley 3U slldably and rotatably mounted upon an electric conducting rod 3| extending between the supports l6 and H. The pulley 30 is rigidly connected by an L-shaped bracket 32, 33 to the slidable iron core 29 and, as at Fig. 1, is disposed approximately adjacent the internal end of the iron core. The arm 32 oi'the bracket is shown as formed of insulating material. The supporting rod 3| is electrically connected by a lead 34 to the metallic bearing sleeve 22.

In operation of the device shown at Fig. 3, electric connection is made to the coil l9 at the hearing sleeve 22 and the contact terminal 26. As. the coil I9 is rotated by the knob 2|, the pulley 30 is constrained to move along the rod 3| by reason of its engagement with the helical coil I9. In so moving, the pulley 30 moves the iron core 29 longitudinally with respect to the coil thereby to maintain the core within only the operative portion of the coil as more or less of the coil is the like- .It is known that such a non-magnetic metallic short-circuited. short-circuiting oi the unused portion of the coil is efiected by connection of the pulley 30 through the rod ti,- the lead 2 3, the sleeve 22, the operating shaft 2%, and the lead 23 to the end of the coil It adjacent the closed end of the coil spool 68.

It is evident that the device of Fig. 3 could be modified in accordance with Fig. 2 by forming the slidably supported core in two sections, the section to the left of the pulley being formed of iron and the section to the right of the pulley being formed of copper or other electric con ducting material.

While I have described only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A variable inductance device comprising a substantially helical coil and a comminuted iron core member mounted for relative axial movement, a variable contact element mechanically mounted in fixed position relative to said core for concurrent movement relative to said coil, said element electrically engaging said coil at a point adjacent one end of said core member, and means including electrical connections to said coil through said contact member to provide an active portion of said coil of selectable inductance disposed on the same side of said point as said core member.

2. A variable inductance device comprising a rotatably mounted substantially helical coil having self-inductance, a comminuted iron core member mounted for relative axial movement with respect to said coil, a variable contact element arranged to engage said coil adjacent one end of said core and in fixed' relation to said core, and means responsive to rotation of said coil to cause said relative axial movement.

3. A variable inductance device comprising a base, a core fixedly mounted-upon said base, a substantially helical coil threadedly mounted upon said base for rotary and longitudinal movement with respect to said core, and an electric contact element mounted upon said base in fixed relation to said core and arranged electrically to disable the portion of said coil withdrawn from.

said core.

a. A variable inductance device comprising a base, a core member having a section of comminuted iron and an adjacent section of nonmagnetizable electric conducting material, a substantially helical coil threadedly mounted upon said base for rotary and longitudinal movement with respect tosaid core, and an electric contact element mounted upon said base in fixed relation to said core and arranged electrically to disable the portion of said coil including said nonmagnetizable core section.

5. A variableinductance device comprising a rotatably mounted substantially helical coil having self-inductance, a core member mounted for relative axial movement with respect to said coil and including adjacent sections of magnetizable material and nonmagnetizable electric conducting material, a contact element mounted in fixed relation with said core and arranged to engage said coil adjacentv the juncture of said nonmagnetizable core sections, and means responsive to movement.

6. A variable inductance device comprising a substantially cylindrical coil having self-induct-' ance, a core member mounted for relative movement along the axis of said coil and including two axially spaced sections one of magnetizable material and the other of non-magnetizable electrically-conducting material, an electrical contact element continuously engaging the turns of said coil and mechanically mounted in fixed position with respect to said core substantially opposite a point between said sections, and means including electrical connections to said coil through said contact element to provide an active coil portion of variable inductance on the same side of said element as said one section and an inactive portion on the opposite side thereof.

'7. A variable inductance device comprising a multi-turn coil having self-inductance, a variable contact element continuously in electrical contact with the turns of said coil, amagnetizable member mounted for relative movement along the axis oi said coil to vary said self-inductance and mechanically positioned fixedly with respect to said element, said member being disposed to have maximum eflect upon said self-inductance to one side of said element, and means including electrical connections to said coil through said element to provide an active coil portion disposed on said one side of said element and to short-circuit the turns of said coil lying on the opposite side of said element.

LAMBERT H. LYNN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,175,554 Bliss Oct. 10, 1939 2,295,348 Leach Sept. 8, 1942 FOREIGN PATENTS Number Country Date 18.935 Great Britain, 1895 Aug. 8, i896 

